Basic Bodice Block

A bodice block (also called a sloper) is a bodice pattern drafted to fit one specific body with no ease beyond what's needed to move, and no style features at all — no collar, no particular neckline, nothing decorative. It's not a garment you'd actually wear. It's a foundation you trace around and modify to create the bodice you actually want, which is a much faster route to a well-fitting garment than adjusting a random pattern from scratch every time.

The dart placement is really the whole story of a bodice block. Front and back both need shaping darts to go from a flat rectangle of fabric to something that follows the curve of a chest and back, and where those darts sit — bust point, shoulder, side seam, waist — determines how the eventual garment will look and move. Once you have a block that fits you, you can rotate a dart from the shoulder to the side seam, or split it into two smaller darts, or convert it into gathering, and the fit underneath stays correct the whole time.

I'd genuinely recommend drafting your own block before you spend much money on commercial patterns. It sounds like a detour, but every future project gets faster once you have one.